Benny and his friend Griffin at Ocean Beach in San Francisco.

Tuesday, June 21, 2011

Bison and Basement Rocks

Yellowstone Day! Ron had never been to the national park before and I hadn't seen it since I was 17. Benny spent the winding trip south to the park carefully ranking all the animals he wanted to see: "First bears, then bison, then antelope ... no, first bison, then bears, then antelope ... wait, there are moose? Okay, first bison, then bears, then moose, then wolves ... oh wait, the antelope ..."

I had cracked open my "Roadside Geology of Montana" again, since the route we chose took us through the length of Paradise Valley between two mountain ranges. I dutifully took pictures of mountains and moraines (those ridges left by the retreat of a glacier) and sandstone ledges, wondering why I bought the darn book. But then we came upon a great roadcut near the southern end of the valley. At Yankee Jim Canyon, the Yellowstone River, which we had been following for much of our travels in Montana, cuts through Precambrian basement rocks. These rocks are the oldest of the old, the rocks formed before life left any traces on earth. Basement rocks, as the name implies, are the bottom layer of the land, and generally considered the last rocks before the mantle (the plastic rock that the earth's plates float on).

Maybe it's the picky editor in me, but I always like to see the basement rocks of a region before I learn about all the mud and sand being laid down and then volcanoes barfing basalt all over the landscape. Montana's basement rocks are about 300 million years old.

Ron stopped the minivan so I could take some closer pictures. Fortunately there was a wide, graveled pullout opposite the roadcut, so I didn't have to take my life into my hands on a narrow shoulder the way I did in the Shenandoah Valley.

These Precambrian basement rocks are complexly folded gneisses (pronounced "nices").

We continued on to Yellowstone, grumbling slightly at signs warning us of a $25 entry fee, and had a nice surprise at the entry point. Since today was the first day of summer, all entry was free! What luck, to hit the most expensive park of the trip on June 21. We started twisting along to Mammoth Hot Springs when we saw a short line of cars pulled off to the side. Someone might have a flat, but generally pulled-over cars in Yellowstone mean one thing: wildlife.

We were not disappointed. Three shaggy bison were grazing by the roadside, unfazed by the vehicles.

We tried to have a picnic lunch at Sheepeater Cliff, but black flies clustered thickly under the trees, where the picnic tables were. So we ate in the minivan again. We haven't had much luck with the picnic lunches on this trip, really. Afterwards we climbed all over the cliff, which is actually basalt lava that broke into columns as it cooled about 500,000 years ago.

We arrived at Old Faithful just as it began its eruption.

And the park said goodbye with a final sighting of wildlife. Probably mule deer.

We stayed the night at a very nice Holiday Inn Express in Jackson Hole, which looked a little forlorn with its ski slopes bare of snow. Tomorrow we head to our ninth state: Idaho.

No comments: